We have a commercial pool it has 4 Pentair intellichlor units. 2 in the upper pipe and 2 in the lower pipe. I had 3 flashing red green and red on the flow switch. I replaced 3 flow switches and 1 came back up fine the other 2 did not. They are still showing the same issue. When I did remove the flow switches 2 of them did not have the metal switch attached the other one had the metal switch but the stem was cracked. Why would only 1 on the upper pipe work and only 1 on the lower pipe work fine. Please advise thank you